Conventional coal feed systems using gravity flow of solids, such as coal feed to coal-fired boilers, can allow major fluctuations in the coal mass flow rate and suspension density.
However, fluctuations of coal mass flow rate to burners within a coal gasification reactor, hereinafter referred to as gasifier, are detrimental to gasifier performance. For example, fluctuations of the coal mass flow rate cause inefficient combustion of fuel within the gasifier and damaging heat fluxes to the burner face within a reaction zone near the burner which result in thermal stresses on the burner face. Since the residence time of the coal within the reaction zone of the reactor is approximately 400 milliseconds or less, the coal mass flow rate should preferably be constant over periods of this order and preferably over shorter periods to maintain constant local conditions. The residence time in the reaction zone determines the upper limit of the range of interest of coal density fluctuations. The response time of a typical process control valve is 10 sec. which determines the lower end of the frequency of interest. Therefore, we are interested in coal flow fluctuations of 0.1-100 Hertz and coal suspension densities of about 50-800 kg/m.sup.3, preferably 200-500 kg/m.sup.3 as is used in the present invention.
Measurement and automatic control of coal mass flow rate to the burners of a gasifier by conventional means are too slow to ensure a constant coal mass flow rate to the burner of a gasifier over time periods as short as 0.4 seconds or less.
The present invention is directed to overcoming this problem in the prior art.
Applicants are not aware of any prior art which, in their judgment as persons skilled in this particular art, would anticipate or render obvious the present invention. However, for the purpose of fully developing the background of the invention, and establishing the state of requisite art, the following art is set forth: U.S. Pat. Nos. 2,779,510; 3,682,511; 4,159,150 and 4,412,762.